Integrated circuits (ICs) are single semiconductor chips comprising arrays of transistors and other built-in components. These gate array structures are typically configured to perform specific logic functions. When the gate array is configured to perform a specific function, an active device is created. Each active device is responsive to at least one input, such that it performs its function in response to the inputs. To function, the active device must be powered, usually from a source off the chip.
When power is applied to an active device in one of the ICs, each of the logic units within the active device is still at its previous state. New inputs into these logic units could result in improper functioning of the active device. Therefore, for an active device to function properly, its logic must be put into a known state. The logic in an active device is put into a known state when reset. After all of the circuitry has been reset, the active device is taken out of reset and is ready to perform its function.
The circuitry required to reset an active device is typically located on the same chip as the active device, and the reset operation is usually triggered by a reset signal derived from a switch on the printed circuit (PC) board or generated by power-on reset circuitry located on the chip. The power-on reset circuitry is often located on a separate chip or made with discrete components on the PC board.
One of the problems associated with power-on reset circuits in the prior art is that the circuits may not, in some instances, fully reset when power was applied to the chip. For example, the parts may be taken out of reset mode before all of the logic is reset, or a short circuit may be created in the logic circuits due to a less than functional voltage appearing on the logic. Short circuits are created, for instance, when an inverter comprises a set of complementary p-channel and n-channel devices serially coupled between power and ground having both gates coupled to the input and both drains coupled to the output. Either device would turn on if it receives either a logical 0 or a logical 1. However, if a voltage on the input of the inverter was between a logical 0 and a logical 1, both devices would conduct, creating a short between power and ground.
The present invention avoids the problems of the prior art power-on reset circuits by providing a reset circuit on the same IC of an active device which generates a reset signal having a sharp edge, such that the logic circuits receives a functional voltage while the reset function is still active. This allows all of the logic of the active device to be reset.